The use of the so-called "posture" chair in business offices is commonplace. There are several types of the so-called "posture" chairs which are utilized for the comfort and convenience of office workers. These chairs vary from the simple secretarial chair where only the back tilts slightly, to the executive posture chair wherein the back tilts to a greater degree than the seat which also may or may not tilt. The shell type chair which is in common usage today provides a completely molded unitary seat, back and arms which tilt as a unit with respect to a pedestal base. This chair, although visually pleasing, because of its unitary construction when tilted lifts the front edge of the seat the same distance away from the floor as the top edge of the back moves toward the floor thus raising the occupant's feet, in many instances, off of the floor and is not completely satisfactory in terms of comfort. Another common chair construction is one in which the seat remains stationary with respect to the pedestal base and the arms remain stationary because of direct connection to the seat, while the back is permitted to tilt at angles of varying degrees generally controlled by a control mechanism. In this type chair, the back moves relative to the arms and if significant overlap is not provided the user can be caught between the back of the chair and the ends of the arms as the back proceeds past the rearward end of the chair arms. This condition is also quite uncomfortable because as the body moves back in relationship to the stationary arms, the user's arms must slide along the upper surface of the chair arms or change their position at the shoulder with respect to the user's body. The most comfortable office type chair in present usage is one in which a sophisticated tilt mechanism of the type disclosed in U.S. Pat. No. 3,603,640 to J. T. Doerner is employed. This type tilt mechanism allows the seat of the chair to tilt at a lesser angle than the chair back tilts through simultaneous movement of both the chair back and the seat at different rates of movement. Although this configuration permits the user's body to remain in more of an L-shaped configuration rather than flattening it out as the stationary seat requires, it also has the deficiency of being used almost solely with chairs whose arms are fixed with respect to the seat and therefore when the back of the chair tilts to a greater degree than the seat, there is still relative movement between the chair back and the chair arms leading to the same kinds of discomfort and possible hazard described with respect to the fixed seat reclining back chair.
In addition to the discomfort factors indicated above with respect to the conventionally employed office seating, mechanical deficiencies are also apparent. In almost every instance, the chair tilt mechanism is located centrally beneath the seat and the back is generally supported from the rearward end of the tilt mechanism centrally of the chair seat through a single central support. This single central support must be of extremely heavy gauge steel in order to support the upper body of heavier chair users. In every instance where the chair arms are connected to the seat whether the seat tilts or not, where there is either a differed degree of movement between the chair back and the chair seat or movement of the chair back only, the arms can only be supported at their lower most ends and when subject to high loads at the upper arm rest portion can fail through the cantilevered action of the loading when lateral force is applied.
An additional problem with much of the office seating available today is that many of the control mechanisms or the central support for the chair back, which may also include externally located height adjustment mechanisms, extend beyond the chair silhouette and because of their heavy metallic construction can cause damage to adjacent office furniture when the chair is easily moved on its casters through direct contact of these parts with such adjacent furniture.